Organic electroluminescent element and lighting device
View Patent ↗An organic electroluminescent element including at least three light-emitting units. The at least three light-emitting units include one or more short-wavelength light-emitting units having a weighted average emission wavelength λ S of 380 or more and less than 550 nm, and two or more long-wavelength light-emitting units having a weighted average emission wavelength λ S of 550 nm or more and 780 nm or less. The two or more long-wavelength light-emitting units are greater in number than the one or more short-wavelength light-emitting units.
1. An organic electroluminescent element, comprising a light transmissive electrode, a light reflective electrode, at least three light-emitting units positioned between the light transmissive electrode and the light reflective electrode,
the at least three light-emitting units comprising:
one or more short-wavelength light-emitting units having a weighted average emission wavelength λ S , indicated by Equation (1) below, of 380 nm or more and less than 550 nm; and
two or more long-wavelength light-emitting units having a weighted average emission wavelength λ S , indicated by Equation (1) below, of 550 nm or more and 780 nm or less,
λ
S
=
∫
380
780
P
(
λ
)
×
λ
d
λ
∫
380
780
P
(
λ
)
d
λ
(
1
)
where P(λ) indicates a spectrum intensity at a wavelength,
the two or more long-wavelength light-emitting units being greater in number than the one or more short-wavelength light-emitting units,
the two or more long-wavelength light-emitting units each being a phosphorescent unit, the one or more short-wavelength light-emitting units each being a fluorescent unit,
each of the at least three light emitting units comprising a light emitting layer, and
each of the at least three light emitting units comprising an electrical charge transfer layer provided on a light reflective electrode side of the light emitting layer.
2. The organic electroluminescent element according to claim 1 , wherein
the at least three light-emitting units include at least one light-emitting unit containing a plurality of light-emitting materials.
3. The organic electroluminescent element according to claim 1 , wherein
a color temperature of a luminescent color is 2500 K or less.
4. The organic electroluminescent element according to claim 1 , wherein
the at least three light-emitting units comprise:
one short-wavelength light-emitting unit, as the one or more short-wavelength light-emitting units; and
two long-wavelength light-emitting units, as the two or more long-wavelength light-emitting units.
5. The organic electroluminescent element according to claim 1 , wherein
a distance d F satisfies conditions of Equation (2) and Equation (3) below, the distance d F being a distance between a light-emitting layer of a light-emitting unit, located the farthest from the light reflective electrode, of the at least three light-emitting units, and the light reflective electrode,
D
F
(
λ
S
)
<
ϕ
(
λ
S
)
×
λ
S
4
π
+
0.75
×
λ
S
(
2
)
D
F
(
λ
S
)
=
n
(
λ
S
)
×
d
F
(
3
)
wherein, in Equation (2), φ(λ S ) indicates a phase shift that occurs in the light reflective electrode, and
in Equation (3), n(λ S ) indicates an average refractive index of a medium that is disposed between the light reflective electrode and the light-emitting layer, for a wavelength of λ S .
6. The organic electroluminescent element according to claim 1 , wherein
a light-emitting unit, located the closest to the light reflective electrode, of the at least three light-emitting units is one of the one or more short-wavelength light-emitting units.
7. The organic electroluminescent element according to claim 1 , wherein
the light transmissive electrode, the at least three light-emitting units, and the light reflective electrode are supported by a substrate, and
the organic electroluminescent element further comprises a light diffusion layer that is disposed between the substrate and the light transmissive electrode.
8. The organic electroluminescent element according to claim 1 , wherein
the at least three light-emitting units include a light-emitting unit containing a green light-emitting material, a light-emitting unit containing a blue light-emitting material, and a light-emitting unit containing a red light-emitting material, which are disposed in this order starting from a side of the light reflective electrode.
9. The organic electroluminescent element according to claim 1 , wherein
the at least three light-emitting units include a light-emitting unit containing a blue light-emitting material, a light-emitting unit containing a red light-emitting material, and a light-emitting unit containing a green light-emitting material, which are disposed in this order starting from a side of the light reflective electrode.
10. A lighting device comprising
the organic electroluminescent element according to claim 1 , and
a housing accommodating the organic electroluminescent element.